Hspec support request

**Describe the feature request**
I have a feature request in Hspec to make it easier to run specific tests with Cabal: https://github.com/hspec/hspec/issues/862

Hspec needs to know if it is run by Cabal.

@sol suggests this can be implemented if `cabal test` sets the environment variable `CABAL_TEST_COMMAND=cabal`

**Additional context**

Currently a failing test will print:

```
To rerun use: --match "/someFailingTest/"
```

To use this suggestion with Cabal, it must be modified to this:
```
cabal test --test-options="--match \"/someFailingTest/\""
```

With this environment variable, Hspec will print out this feedback for Cabal.

Start at the `cabal test` entry point and trace how its test processes receive environment variables. Check the linked Hspec issue for the expected behavior. Done means `cabal test` provides `CABAL_TEST_COMMAND=cabal` so Hspec can print a Cabal-specific rerun command.

Written by the indexing model from the issue text.